Fire doors are designed and installed in an attempt to protect lives and property from fire, smoke, and heat by providing a barrier to withstand the fire, smoke, and heat for a period of time. To be labeled or certified as a fire door, a door must fulfill the requirements of certain codes or standards that regulate the construction and installation of such doors. These codes or standards include, among others, the Uniform Building Code (UBC), and codes promulgated by the National Fire Protection Association (NFPA), and American Society for Testing and Materials (ASTM).
Private testing laboratories, such as Underwriters' Laboratories and Warnock Hersey, may test for adherence to such codes or standards, and may test for additional attributes. The laboratories may also certify that a fire door meets fire protection requirements after conducting testing (such as destructive testing) of the door. Usually, this certification is expressed as a fire-rating offering a specific level of protection from fire, smoke, and/or heat for a limited amount of time. For example, a 20-minute fire-rated door should, if installed correctly, maintain its structural integrity and provide a barrier to fire, heat, and/or smoke for at least 20 minutes. So long as a door meets relevant fire protection requirements, its design may vary to fulfill other design considerations, such as weight, cost of manufacture, and aesthetic appearance.
An interior routed medium-density fiberboard (MDF) fire door meeting current fire protection requirements generally is constructed of a one-and-one-half inch thick sheet of MDF having a minimum density of approximately 42 pounds per cubic foot (pcf) and a one-eighth of an inch hardboard skin on both sides of the MDF. A single-swing wood fire door using MDF having this thickness and density, and that is three feet wide by eight feet high, weighs nearly 153 pounds. Not only is such a door extremely heavy, but manufacturing it can be costly and difficult as well.
For example, manufacturing a molded-panel fire door that meets current fire protection requirements generally requires using a mold. There are several ways known to prepare molds. One common method is to use matching castings or dies. A molded door generally has two exterior skins, and one mold is required for each skin. To make a custom-ordered door, a new mold must be created. While using molds to make a paneled door is generally less costly on a high-volume basis than machining reliefs into a door, molding custom-ordered doors can significantly add to the manufacturing expense—in some cases, this expense can become cost-prohibitive.
Manufacturing paneled wood doors without molds is known in the art. Such doors generally include two exterior skins with a core inserted between the skins. In one such conventional door, the core generally includes a three-eights-of-an-inch-thick layer of MDF, a three-eights-of-an-inch-thick layer of expanded polystyrene, and another three-eights-of-an-inch-thick layer of MDF. The layers of the core are adhered to one another, as are the external skins and the core. Wood side stiles and top and bottom rails are then adhered to an outer perimeter of the door. Panels are formed by routing a series of grooves into the external skins.